JPH1175368A - Multioutput switching regulator - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent an office automation apparatus connected to an output terminal from malfunctioning at a low cost and easily, by making constitution so as to supply, from a second switching element, a divided voltage obtained by dividing the terminal voltage of a first or second output terminal. SOLUTION: A voltage-dividing means for the terminal voltage of an output terminal V1 is composed of a resistor R2 and a Zehner diode ZD1, and the divided voltage is connected to the emitter of a transistor Q4 as an input. If the transistor Q4 is turned off here, the terminal voltage of the output terminal V1 lowers, a transistor Q3 turns off, and a switching element Q2 does not turn on. Consequently, it becomes possible to prevent the output switching element Q2 from malfunctioning, and it becomes possible to prevent an abnormal voltage from inputting to an office automation apparatus, etc., connected to the output terminal V1. Accordingly, it becomes possible to prevent the office automation apparatus, etc., from malfunctioning, and to obtain a high-reliability high-safety multioutput switching regulator.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an output switch of a multiple output switching regulator.

[0002]

2. Description of the Related Art In recent years, OA equipment has been diversified and multi-functional, and the like, and the switching regulator has been developing in the direction of multi-output. ON of each output for etc.
The / OFF control function is becoming a necessary condition. Conventionally,
A multi-output switching regulator used as a power supply in OA equipment or the like is configured, for example, as shown in FIG.

That is, a DC input 1 is intermittently supplied to a primary winding of a transformer T1 by a switching element Q1 such as an FET, and is converted into a predetermined voltage by the transformer T1. Then, the plurality of AC outputs output from the secondary winding of the transformer T1 are converted into a rectifier diode D1 and a smoothing capacitor C.
1, rectifier diode D2 and smoothing capacitor C2,
The DC voltage is converted by the rectifying diode D3 and the smoothing capacitor C3, and a required DC current output is obtained at the output terminals V1, V2, V3.

An output switch element Q2 such as an FET is provided between the output terminal V2 and a rectifying / smoothing circuit including a diode D2 and a capacitor C2. The gate of the output switch element Q2 is connected to an output terminal V1 via a gate resistor R1.
And supplies a gate drive current for turning on the output switch element Q2. Further, a transistor Q3 for controlling ON / OFF of the output switch element Q2 is connected to the gate of the output switch element Q2.
And the emitter is connected to the GND terminal. Further, the base of the transistor Q3 is connected to the collector of the transistor Q4, and the emitter of the transistor Q4 is connected to the output terminal V3. The base of the transistor Q4 is connected to the output switch ON / OFF signal input terminal 3.

For example, an output switch ON / OFF signal R
The ON signal (High level) to the AM terminal 3 is 5
[V], OFF signal (Low level) is 0 [V]. When an ON signal is input to the output switch ON / OFF signal input terminal 3, the transistor Q4 is turned off. Then, the transistor Q3 is turned off, and the output switch element Q
2, a gate drive current is supplied, and the output switch element Q2 is turned on.

Conversely, when an OFF signal is input to the output switch ON / OFF signal input terminal 3, the transistor Q4 is turned on, the transistor Q3 is turned on, and the gate charge of the output switch element Q2 is pulled out to drive the gate. Since the current cannot be supplied, the output switching element Q2 is turned off, and the output of the output terminal V2 becomes O
It becomes FF. In the multi-output switching regulator having the above-described configuration, the output is turned on before the output terminal V2.
Although an output switch element Q2 for turning on / off is provided, this output switch is extremely useful in practical use.

That is, the output switch is often controlled by an OA device or the like connected to the output terminal.
When an OA device connected to the output terminal is in a standby state, the output that does not require a load current is turned off, thereby enabling independent supply power to each function, power saving, a protection function, and the like. Become. However, the multi-output switching regulator having the above configuration has the following problems.

[0008]

That is, in the multi-output switching regulator having the above-described configuration, an output switch which is extremely useful in practical use is provided at a stage preceding the output terminal, but this output switch is mainly connected to the output terminal. It is often controlled by OA equipment or the like.

For example, when the OA equipment or the like connected to the output terminal is in a standby state or the like, a load is required only for the normal output terminal V3, and the output terminals V1 and V2 are required.
Is a state near no load. Further, an output switch O is provided for independent power supply to each function, power saving, protection function, and the like.
When an OFF signal is input to the N / OFF signal input terminal 3, the output to the output terminal V2 is turned off because the output switching element Q2 is turned off.

[0010] At this time, if the DC input 1 is cut off due to the supply of electric power from the primary side, that is, the outlet is disconnected, the supply of electric power to the secondary side is stopped, and the load is applied to the output terminal V3. Is connected, the electric charge stored in the smoothing capacitor C3 is also immediately discharged, the power supply from the output terminal V3 is stopped, and the OA device or the like connected as a load stops functioning. I will.

However, since the output terminal V1 is in a state close to no load, it takes time for the electric charge stored by the smoothing capacitor C1 to escape. Naturally, the charge is also stored in the smoothing capacitor C2,
Since the output switch element Q2 is OFF, there is no path through which the electric charge escapes.
A predetermined voltage is generated on the drain terminal side (input side) of No. 2.

When such a state occurs, the voltage of the output terminal V3 drops instantaneously,
The transistor Q4 turns off. Then, the transistor Q3 is turned off and the output switching element Q2 is turned on, that is, an output voltage is output to the output terminal V2.

Therefore, although the OFF signal is input to the output switch ON / OFF signal input terminal 3, the output switch element Q2 malfunctions and the output voltage is output to the output terminal V2. An abnormal voltage is input to the OA equipment connected to the output terminal of the multi-output switching regulator.
There is a danger that the equipment will break down.

The present invention has been made in consideration of such problems of the prior art, and an object of the present invention is to simplify and reduce the cost of OA equipment connected to an output terminal. It is another object of the present invention to provide a multi-output switching regulator which can be avoided by the above.

[0015]

SUMMARY OF THE INVENTION In order to achieve the above object, the present invention provides a method of intermittently converting a DC input to a predetermined voltage by a transformer by switching the DC input, and converting a plurality of AC outputs from the transformer to a plurality of rectifiers. In a multi-output switching regulator that performs rectification and smoothing by a smoothing circuit and outputs to at least two output terminals, the switching regulator is provided between the rectification and smoothing circuit and the second output terminal, and is connected to a first output terminal via a resistor. An output switch element having an ON / OFF control input terminal, and an ON / OFF control terminal of the output switch element for controlling ON / OFF of the output switch element;
A first switch element having an ON / OFF control input terminal; and an ON / OFF control input connected to the ON / OFF control input terminal of the first switch element so as to control ON / OFF of the first switch element. A second switch element having a terminal; and an ON / OFF control input terminal of the second switch element to control ON / OFF of the output switch element via the second switch element and the first switch element. A connected output switch ON / OFF signal input terminal;
Voltage dividing means for dividing the terminal voltage of the first or second output terminal, wherein the second switch element is configured to be supplied with the divided voltage of the voltage dividing means. It employs a characteristic multi-output switching regulator.

The output switch element is an FET, its ON / OFF control input terminal is a gate, the first switch element is a first transistor, its ON / OFF control input terminal is a base,
The collector of the first transistor is connected to the gate of the output switch element, the second switch element is the second transistor, its ON / OFF control input terminal is the base, and the collector of the second transistor is the first transistor. Preferably, it is connected to a base, and a divided voltage of the voltage dividing means is connected to an emitter of the second transistor.

Further, it is preferable that the voltage dividing means divides the voltage on the input side of the output switch element, and the voltage dividing means is constituted by a resistor and a Zener diode, or is constituted by two resistors. .

[0018]

The multi-output switching regulator having the above-described configuration has the following operation when the OA device or the like connected to the output terminal is in a standby state or the like. That is, when the signal of the output switch element OFF is input to the output switch ON / OFF signal input terminal which is an external signal input terminal, a load is always required when the DC input is cut off such as disconnection of an outlet. By taking the reference voltage of the output switch circuit from the output terminal close to no load instead of the output terminal that is assumed to be erroneous, the malfunction of the output switch element is eliminated, so that an abnormal voltage for the OA equipment etc. connected to the output terminal Since no input is made, a failure of the OA equipment or the like can be avoided.

[0019]

Embodiments of the present invention will be described below with reference to the drawings. Embodiment 1 FIG. 1 is a circuit diagram of a multi-output switching regulator according to Embodiment 1 of the present invention. In FIG. 1, the same reference numerals as those used in FIG. 3 indicate the same or corresponding elements. In FIG. 1, the difference from the prior art is that the means for dividing the terminal voltage of the output terminal V1 is constituted by a resistor R2 and a Zener diode ZD1, and the divided voltage is input to the emitter of the transistor Q4. is there.

For example, it is assumed that an output OFF signal is input to the output switch ON / OFF signal input terminal 3 when the OA equipment connected to the output terminal is in a standby state (standby) or the like. At this time, if the DC input is cut off, such as when the outlet is disconnected, the power supply from the primary side stops. Since the output terminal V3 always requires a load, the voltage instantaneously drops. However, since the output terminal V1 is in a nearly no-load state, it takes time for the charge of the smoothing capacitor C1 to escape. Similarly, the output of the output terminal V2 is output from the output switch element Q2 which is OFF. Since power is not supplied to the output terminal V2, it takes time for the charge of the smoothing capacitor C2 to escape.

In order to maintain the output switch element Q2 in the OFF state, the transistor Q3 is turned on and
The transistor Q4 needs to be ON. At this time,
Since the resistor R2 and the Zener diode ZD1, which are voltage dividing means, divide the terminal voltage of the output terminal V1, when the transistor Q4 turns off, the terminal voltage of the output terminal V1 decreases. Then, the transistor Q4 is turned off.
F, the transistor Q3 is turned off and the output switching element Q2 is about to be turned on. However, since the terminal voltage of the output terminal V1 has already been reduced, it is possible to supply a drive current to the gate of the output switching element Q2. Therefore, the output switch element Q2 does not turn on.

Therefore, by employing the circuit configuration shown in FIG. 1, malfunction of the output switch element Q2 can be prevented, and an abnormal voltage is not input to the OA equipment connected to the output terminal. A failure of OA equipment or the like can be avoided, and a highly reliable and safe multi-output switching regulator can be provided.

(Embodiment 2) FIG. 2 is a circuit diagram of a multi-output switching regulator according to Embodiment 2 of the present invention. In addition,
2, the same reference numerals as those used in FIG. 1 indicate the same or corresponding elements. In FIG.
The difference from the above is that the means for dividing the terminal voltage on the drain side of the output switch element Q2 is constituted by resistors R2 and R3, and the divided voltage is input to the emitter of the transistor Q4.

As in the first embodiment, when the OA device connected to the output terminal is in a standby state (standby) or the like, an output OFF signal is input to the output switch ON / OFF signal input terminal 3. Since the resistors R2 and R3, which are voltage dividing means, divide the terminal voltage on the drain side of the means switching element Q2, when the transistor Q4 turns off, the terminal voltage on the drain side of the output switch Q2 decreases. doing. Then, the transistor Q4 turns off, the transistor Q3 turns off, and the output switch element Q2 tries to turn on.

However, when the time until the terminal voltage on the drain side of the output switching element Q2 decreases and the time until the output terminal V1 decreases are compared, the smoothing capacitor C
1 or C2, which is determined by whether there is a path through which the charge stored in the output terminal V1 is directly connected to the load and the output voltage of the output terminal disconnected from the load by the output switching element Q2. Of the terminal voltages of the switching element Q2, the terminal voltage of the output terminal V1 is often shorter in time until the output voltage decreases.

At this time, the transistor Q4 is turned off, the transistor Q3 is turned off, and the output switch element Q2
Is turned on, the terminal voltage of the output terminal V1 is low, so that the drive current cannot be supplied to the gate of the output switch element Q2.
There is no N.

Further, even if the output switching element Q2 is ON
Even if this is done, no voltage is output to the output terminal V2 because the terminal voltage on the drain side of the output switching element Q2 has already dropped. Therefore, malfunction of output switch element Q2 can be prevented, and OA connected to the output terminal can be prevented.
Since an abnormal voltage is not input to the device or the like, a failure of the OA device or the like can be avoided, and a highly reliable and safe multi-output switching regulator can be provided.

Further, even in comparison with the first embodiment, since the Zener diode is replaced with a resistor, it is more effective in reducing the cost. It is clear that the same effect can be obtained even when the first embodiment is applied to the multi-output switching regulator described in the second embodiment, and the present invention is not limited to the above-described embodiment and does not depart from the gist of the present invention. Obviously, the range can be changed.

[0029]

Since the present invention is configured as described above, it has the following effects. The malfunction of the output switch element Q2 can be prevented, and the OA connected to the output terminal can be prevented.
Since an abnormal voltage is not input to the device or the like, a failure of the OA device or the like can be avoided, and a highly reliable and safe multi-output switching regulator can be provided.

[Brief description of the drawings]

FIG. 1 is a circuit diagram of a multi-output switching regulator according to a first embodiment of the present invention.

FIG. 2 is a circuit diagram of a multi-output switching regulator according to Embodiment 1 of the present invention.

FIG. 3 is a circuit diagram of a conventional multi-output switching regulator.

[Explanation of symbols]

Reference Signs List 1 DC input 2 Controller 3 Output switch ON / OFF signal input terminal Q1 Switching element Q2 Output switching element Q3, Q4 Transistor T1 Transformer D1, D2, D3 Rectifying diode C1, C2, C3 Smoothing diode R1 Gate drive resistor R2, R3 , ZD1 Voltage dividing means V1, V2, V3 Output terminal GND Ground terminal

Claims (5)

[Claims] 1. A multi-input circuit comprising: a DC input and an output which are intermittently converted by a switching means and converted into a predetermined voltage by a transformer; In the output switching regulator, an ON / O provided between the rectifying and smoothing circuit and the second output terminal and connected to the first output terminal via a resistor.
An output switch element having an FF control input terminal; and a first switch connected to the ON / OFF control terminal of the output switch element so as to control ON / OFF of the output switch element, and having an ON / OFF control input terminal. An element, a second switch element having an ON / OFF control input terminal connected to the ON / OFF control input terminal of the first switch element so as to control ON / OFF of the first switch element; An output switch ON / OFF signal input terminal connected to the ON / OFF control input terminal of the second switch element so as to control ON / OFF of the output switch element via the two switch element and the first switch element And dividing the terminal voltage of the first or second output terminal. A voltage dividing means, wherein the second switch element is configured to be supplied with a divided voltage of the voltage dividing means. 2. The multi-output switching regulator according to claim 1, wherein the output switching element is an FET, an ON / OFF control input terminal is a gate, a first switching element is a first transistor,
The ON / OFF control input terminal is a base, the collector of the first transistor is connected to the gate of the output switch element, the second switch element is the second transistor, and the ON / OFF control input terminal is the base. And the collector of the second transistor is the first
A multi-output switching regulator connected to a base of a transistor, wherein a divided voltage of the voltage dividing means is connected to an emitter of a second transistor. 3. The multi-output switching regulator according to claim 1, wherein the voltage dividing means divides a voltage on an input side of the output switching element. 4. The switching regulator according to claim 1, wherein said voltage dividing means comprises a resistor and a Zener diode. 5. The multi-output switching regulator according to claim 1, wherein said voltage dividing means comprises two resistors.